1. Field of the Invention
The present invention relates to a resin-encapsulated semiconductor device wherein a semiconductor chip is encapsulated by an encapsulating resin.
2. Description of the Related Art
Recently, there have been developed a thin resin-encapsulated package for a surface mounting such as a quad flat package (QFP), a plastic-lead chip carrier (PLCC), and a small outline J-bent package (SOJ) with an increase in density of a semiconductor device.
These resin-encapsulated semiconductor devices generally have a structure in which a semiconductor chip is encapsulated by various kinds of encapsulating resins. Detailedly, a semiconductor device is encapsulated in such a state that semiconductor chip is mounted on a die pad of a lead flame with a die bonding portion interposed, and furthermore, a bonding pad on the upper surface of the semiconductor chip is connected electrically with an inner lead of the lead flame by a bonding wire.
When being mounted on the substrate, these resin-encapsulated semiconductor device is left in such a high temperature condition as about 200.degree. C. or more. At that time, since moisture absorbed in the inner part of the encapsulating resin layer is abruptly vaporized to generate a high pressure, if, for example, there is any pealed portion due to poor bonding in the interface between respective members in the inner part of the encapsulating resin layer, expansion or cracks are caused and the reliability to the moisture resistance is extremely deteriorated.
In order to solve these problems, there have been proposed various methods, for example, a method disclosed in Japanese Unexamined Patent Publication No. 63-179554, in which an adhesiveness between a die pad and an encapsulating resin layer is improved by forming a polyimide-based resin film on the lower surface of the die pad, a method disclosed in Japanese Unexamined Patent Publication No. 1-261853, in which by interposing an adhesive resin film in the interface between the whole surface of the inner lead, the lower and side faces of the die pad, the whole surface of the bonding wire, and the upper and side faces of the semiconductor chip and the encapsulating resin layer, an adhesiveness between the above-mentioned respective members and the encapsulating resin is improved, and a method disclosed in Japanese Unexamined Patent Publication No. 3-22465, in which by forming a polyimide-based resin film on the upper face of the semiconductor chip and on the lower face of the die pad, an adhesiveness between these members and the encapsulating resin layer is improved.
These methods, however, cannot improve an adhesiveness of the interface between the die pad and the die bonding portion where the adhesiveness is especially readily deteriorated, due to the intrusion of the water absorbed through the interface between the lead frame and the encapsulating resin layer. In the die bonding portion, there have been conventionally selected materials which can mitigate the stress caused by the difference of the thermal expansion coefficient between a semiconductor chip and a die pad. When such materials are used in the die bonding portion and a semiconductor chip is simply mounted through the die bonding portion, an adhesiveness in the said interface is extremely deteriorated in the high temperature and high humidity condition. Therefore, pealing is caused in the interface between said die bonding portion and the die pad at the time of surface mounting, and finally, expansion and cracks in the encapsulating resin layer are caused.
Furthermore, in such a semiconductor device, there are some problems, in many cases, in the property of the die bonding agent which forms the die bonding portion. As a die bonding agent, there have conventionally used in general a resin paste in which a curing agent, a reactive diluent, a low stress-imparting agent, a solvent, an electroconductivity-imparting agent and the like are incorporated into a resin such as an epoxy resin and a polyimide-based resin. In a conventional resin-encapsulated semiconductor device which uses such a die bonding agent, however, thermal stress is unevenly imposed on the semiconductor chip particularly in the heat-refrigerating step at the surface mounting process to cause pealing in the interface between the semiconductor chip and the die bonding portion, and expansion and cracks are easily caused in the encapsulating resin layer.